1. Field of the Invention
The present invention relates to a read head with improved lead layers and, more particularly, to lead layers that have planar high and low resistance lead layer portions wherein the high resistance lead layer portions have improved dimensions and performance.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS to cause the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A magnetic gap is formed between the first and second pole piece layers by a write gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing information in tracks on moving media, such as in circular tracks on a rotating disk.
The read head includes first and second shield layers, first and second gap layers, a read sensor and first and second lead layers that are connected to the read sensor. The first and second gap layers are located between the first and second shield layers and the read sensor and the first and second lead layers are located between the first and second gap layers. The distance between the first and second shield layers determines the linear read density of the read head. Accordingly, the first and second gap layers are constructed as thin as possible without shorting the lead layers to the first and second lead layers. High linear density results in more bits being read by the read head per length of magnetic track passing by the read bead on the rotating disk.
Each of the first and second leads has a high resistance lead layer and a low resistance lead layer which means that the resistance of the high resistance layer is higher than the resistance of the low resistance layer. Each high resistance lead layer is a material that is resistant to corrosion since it has an edge exposed at the air bearing surface. The high resistance lead layer typically includes a film made of tantalum (Ta). Each low resistance lead layer is corrosive, but this is of no consequence since it is protected from the outside environment by being recessed in the head. The low resistance lead layer typically includes a film made of copper (Cu) or gold (Au).
The high resistance layer has multiple films. One of the films is the Ta film for conducting a sense current through the read sensor. Another one of the films is a hard bias film for longitudinally biasing the read sensor so that it is magnetically stabilized to prevent Barkhausen noise. In the past each high resistance lead layer extended from a respective side edge of the read sensor in a lateral direction (parallel to the ABS) before it extended back into the head to make contact with the low resistance lead layer. The longer the extension of the high resistance lead layer the thicker the high resistance lead layer has to be in order to maintain its resistance at an acceptable level. When the resistance gets too high the read head is damaged by heat. When the extension of the high resistance lead layer is made thicker in order to keep its resistance down planarization between the top surfaces of the read sensor layer and the high resistance lead layers is degraded.
The read sensor is bounded by a front edge at the ABS, first and second side edges that extend perpendicular to the ABS and a back edge that is spaced from the ABS and that defines a stripe height of the read head. Each high resistance lead layer has a forward edge that makes contact with a respective one of the first and second edges of the read sensor and is described in commonly assigned U.S. Pat. No. 5,018,037 which is incorporated by reference herein. This type of connection is referred to in the art as a contiguous junction. When the high resistance lead layers are thickened in order to reduce resistance their top surfaces are elevated with respect to the top surface of the read sensor. This causes a step adjacent each side edge of the read sensor. Unfortunately, these steps are replicated through the second gap layer and the second shield/first pole piece layer all the way to the write gap layer of the write head which may cause the write gap layer to be curved. The curved write gap layer causes the write head to write curved bits (magnetic signals) on the rotating track. When the straight across read head reads these curved bits it progressively loses magnetic intensity from a center of the bit toward outer edges of the track. Accordingly, there is a strong felt need to promote planarization of the read sensor and the high resistance leads so as to reduce write gap curvature.
We sought a method to construct the lead layers that would promote planarization between the read sensor and the high resistance lead layers at the ABS. One method investigated constructs the high resistance lead layers before defining a stripe height of the sensor by milling. In this method read sensor material layer is deposited over an entire wafer. A first mask is formed that has openings at the high resistance lead layer sites which extend to the first and second side edges of the read sensor. Read sensor material is milled out at the high resistance lead layer sites and the high resistance lead layer material is deposited to form first and second high resistance lead layers at the high resistance lead layer sites that make contiguous junctions with the first and second side edges of the read sensor. This establishes the track width of the read. Track width density (number of tracks per inch of the magnetic disk) times the aforementioned linear density is the areal density of the read head. Increasing the areal density increases the bit density (number of bits per square inch of the magnetic medium) of the disk drive. The first mask is removed and a second mask is formed that covers the read sensor and the high resistance lead layers. All exposed read sensor material is then milled away to define the back edge and stripe height of the read sensor. The stripe height is important in establishing the magnetics of the read sensor. The second mask is then removed and a third mask is formed that has openings at low resistance lead layer sites. Low resistance lead layer material is then deposited that forms first and second low resistance lead layers that overlap and engage the first and second high resistance lead layers. The third mask is then removed.
Unfortunately, the aforementioned method alters the high resistance lead layers when the stripe height of the read sensor is defined. Since the second mask must be slightly inboard of the outer edges of the high resistance layers in order to ensure complete removal of unwanted read sensor material, an outer edge portion of each high resistance lead layer is subjected to milling. Reduction of the high resistance layers due to this milling requires that the thickness of the high resistance layers be increased as deposited in order to satisfy the resistance requirements. As stated hereinabove, thicker high resistance leads results in increased write gap curvature. Accordingly, there is a strong felt need to provide a method of making the read sensor leads that will not contribute to thicker high resistance lead layers.